Biological samples may be preserved by cryogenic freezing. The biological samples are usually stored in disposable containers (disposables). The shape of the disposable container used depends on the type of sample. Examples of commonly used disposable containers include vials, straws and bags. The disposable container is stored at low temperatures in a Dewar flask typically filled with liquid nitrogen at a temperature of −196° C.
Where samples are stored in straws, a plurality of straws are usually kept in a visotube, a plurality of visotubes are in turn typically kept in a goblet, and a plurality of goblets are kept in a canister which is stored in the Dewar.
Stored biological samples can be identified by writing on the disposable containers themselves, or by labels stuck to the containers. These labels may be handwritten or printed and can include bar codes. However, such methods of identification have associated disadvantages; written notes on containers can easily be erased or smudged and labels containing handwritten notes and printed text or barcode information can fall off the disposable containers while they are stored inside the Dewar leading to unidentifiable samples. These problems are exacerbated by the cold conditions in which biological samples must be kept.
When performing an audit of biological samples stored in cold storage (at temperatures of −196° C.), the samples should not be allowed to warm up to a temperature greater than −130° C. It is therefore desirable to minimise the amount of time spent outside of the Dewar wherever possible.
Recording, monitoring and auditing of samples in cold storage takes a considerable amount of time and effort, even when samples are labelled using barcodes. An additional and undesirable increase in the time taken to record or audit samples arises as a result of frost which forms on the surfaces of disposable containers and their labels when they are removed from liquid nitrogen into relatively warmer temperatures. It is common for samples to be stored for many years (e.g. 15 years) but even after just one year in storage, the layer of frost which builds up on a disposable container can make it impossible to make an optical reading of a bar code on a label using a bar code reader because a layer of frost blocks or diffracts the light of the bar code reader. The container cannot be warmed up to remove frost as this would lead to destruction of the sample. The frost can be wiped off the disposable container but this contributes to an undesirable increase in the amount of time taken to read the sample.
It is known that Radio Frequency ID (RFID) tags can be used to monitor a plurality of disposable containers stored at low temperatures of down to −196° C. An RFID reader can be used to write information to and read information from the RFID tag before, after, or during cryogenic storage.
An RFID tag includes an RF transmitter and an RF receiver. An RFID reader can be used to transmit an encoded radio signal to a tag to interrogate it. Upon receiving the interrogation signal, the RFID tag transmits its identification information to the reader. This identification information may be a unique serial number assigned to a particular patient or a particular sample.
In Europe and other countries outside of the US, RFID components for medical storage operate at an approved frequency of 13.56 MHz. It is important that the frequency used for the RFID tag does not lead to any undesirable interference with other electronic medical equipment. Lower medically approved frequency bands such as 125 KHz do not provide enough signal bandwidth to provide the tag with a useful user defined memory.
EP2315163 discloses RFID tags that can be inserted into straws. Biological material is drawn into a straw via a “sucking” process. The location of an RFID tag in a straw takes up space inside of the straw. In addition, the placement of an RFID tag inside the straw impedes the ability to draw air and the material from container to straw, regardless of which end of the straw the RFID tag is inserted with respect to the sucking action. The location of the RFID tag inside the straw also means that the size of RFID tag used must be limited to a size smaller than the inner diameter of the straw.
WO 2005/115621 describes tagging of cryogenic straws using write-on or printable adhesive labels having an RFID tag attached thereto or incorporated therein. This method has the disadvantage that it relies upon the adhesive label retaining its adhesive properties. The longer the straw is kept under cryogenic conditions and the more times the goblet of tubes is accessed, the more likely it is that the adhesive will fail. In addition, the label is usually stuck to the straw by hand. A significant amount time and considerable amount of care is required to ensure that the adhesive label is correctly applied and therefore less likely to fall off during storage.